1. Field of the Invention
The invention relates to mouth rinses and dentrifices which ordinarily impart a harsh taste and astringency to the mouth. More particularly, the invention relates to eucalyptol and zinc containing oral hygiene compositions wherein the burning sensation and astringency of such products is masked.
2. Description of Related Art
Mouth rinses, especially mouth washes, containing essential oils are well-known in the art of oral hygiene. For example, U.S. Pat. No. 4,945,087 is believed to be directed to the commercial product known as COOL MINT LISTERINE.RTM.. U.S. Pat. No. 4,945,087 teaches a mouth wash comprising the essential oil known as thymol which is utilized for its antimicrobial activity. The patent teaches that the thymol imparts a harsh or medicine-like taste to mouth rinses and that it would be desirable to mask this taste. For this purpose, the patent utilizes a composition containing a mixture of sugar alcohols and anethole. As an optional ingredient in the mouth rinses disclosed by U.S. Pat. No. 4,945,087, a large number of different types of surfactants are mentioned. One type of non-ionic surfactant mentioned as an optional ingredient is an ethoxylated hydrogenated castor oil (col. 4, lines 32-46), however, there is no teaching of any function of this material other than for its known function as a surface active agent (ie., surfactant). It is only through the use and manipulation of the sugar alcohols and the anethole that masking of the thymol taste is taught to be accomplished.
Another component of the commercial mouthwash LISTERINE.RTM.which is effective for its antimicrobial activity is eucalyptol (see U.S. Pat. No. 4,945,087, col. 3, lines 4-14 which discloses the possibility of using eucalyptol in addition to thymol). U.S. Pat. No. 4,945,087 attributes the harsh or medicinal taste of the product exclusively to thymol. Eucalyptol is not blamed by the patent as being responsible for or contributing to this problem. Although not appreciated or recognized by U.S. Pat. No. 4,945,807, it was subsequently discovered by the present inventors that the burning sensation of LISTERINE.RTM. is principally due to the eucalyptol, rather than the thymol. Accordingly, proposed solutions for masking the taste of thymol, such as the one taught in U.S. Patent 4,945,087, have not proved to be particularly effective for masking the burning sensation of eucalyptol containing mouth rinses such as LISTERINE.RTM..
Another common antimicrobial agent used in oral hygiene rinses is zinc, typically added as a zinc salt. For example, European Patent Publication 0 251 542 teaches a mouth wash containing zinc chloride. However, the zinc salt is known to impart undesirable astringency to the mouth rinse. In order to abate the astringency, European Patent Publication 0 251 542 teaches the use of 0.1% to 5% by wt. polyoxyethylene hydrogenated castor oil. However, European Patent Publication 0 251 542 is not directed to eucalyptol containing mouth rinses, and the reference does not teach any means for masking the burning sensation imparted by eucalyptol containing mouth rinses.